The present invention relates generally to filled aqueous polymer latices such as those used for carpet backing and roofing, and more particularly relates to surfactants and/or borate compounds used to stabilize the viscosity of aqueous polymer latices that include fly ash or fly ash blends.
Aqueous polymer dispersions or latices consist of small particles of polymers, typically ranging in size from 60 nm to 250 nm, dispersed in water. They are typically produced using emulsion polymerization, and can be used in a wide range of industrial applications, including carpet backing, seal coatings, waterproofing membranes, fabric sizing and reinforcement, automotive components and adhesives. These polymer dispersions often utilize a mineral filler or extender to impart desired mechanical properties and to reduce raw material costs. Exemplary mineral fillers include calcium carbonate, aluminum trihydrate (aluminum hydroxide), kaolin (aluminum silicate dihydrate), talc, mica, wollastonite, silica, glass flakes and glass spheres.
Recently, there has been an increased interest in using fly ash as a filler in aqueous polymer latices. In particular, because fly ash is a recycled material produced by the combustion of coal, fly ash qualifies as a recycled material and thus is desirable for this reason. Furthermore, fly ash has been found to be a particularly useful filler for polymer composites as described, for example, in U.S. Pat. Nos. 6,695,902 and 6,916,863, which are hereby incorporated by references in their entirety.
Conventional latex systems used in the carpet industry as adhesive backing materials are low viscosity, aqueous compositions that are applied at high carpet production rates and preferably offer good fiber-to-backing adhesion, tuft bind strength and adequate flexibility. Generally, excess water is driven off and the latex is cured by passing through a drying oven. Styrene butadiene rubbers (SBR) are the most common polymers used for latex adhesive backing materials. Typically, the latex backing system is heavily filled with an inorganic filler such as calcium carbonate or aluminum trihydrate. The latex systems used in the carpet industry may further include other ingredients such as antioxidants, antimicrobials, flame retardants, smoke suppressants, wetting agents, anti-foaming agents, frothing agents and rheology modifiers.
Practical use of fly ash as a filler in aqueous polymer latices has been limited, however, due to adverse Theological effects in adding fly ash to an aqueous polymer latex. Specifically, adding fly ash to an aqueous latex can result in a significant increase in the viscosity of the latex formulation, to 50,000 centipoise (cP) or more, over time. A significant increase in the viscosity of a formulation can lead to difficulty in storing, processing, or applying the aqueous latex formulation. Specifically, a liquid with a viscosity of more than 30,000-40,000 cP is difficult to pump or otherwise transport into and out of tanks and other processing equipment. As a result the formulation may need to be removed manually, e.g., by shoveling it out of the storage unit. Furthermore, manufacturers using an aqueous polymer latex may have viscosity limits or specifications to ensure product quality (i.e. uniform thickness of application) and thus increases in viscosity caused by the use of a fly ash as a filler would be undesirable.
Because of above discussed limitations in processing or applying aqueous polymer dispersions that have experienced a significant viscosity increase over time, it would be desirable to minimize the rise in the viscosity of an aqueous polymer latex so that it can be stored for one or more days and even over a week and can be processed and/or applied to a substrate as a desirable viscosity.